The Arduino Reference text is licensed under a Creative Commons Attribution-Share Alike 3.0 License.

Find anything that can be improved? Suggest corrections and new documentation via GitHub.

Doubts on how to use Github? Learn everything you need to know in this tutorial.

Last Update: Not Available

Edit This Page
Reference > Language > Variables > Variable scope qualifiers > Const

const

[Variable Scope & Qualifiers]

Description

The const keyword stands for constant. It is a variable qualifier that modifies the behavior of the variable, making a variable "read-only". This means that the variable can be used just as any other variable of its type, but its value cannot be changed. You will get a compiler error if you try to assign a value to a const variable.

Constants defined with the const keyword obey the rules of variable scoping that govern other variables. This, and the pitfalls of using #define, makes the const keyword a superior method for defining constants and is preferred over using #define.

Example Code

const float pi = 3.14;
float x;
// ....
x = pi * 2; // it's fine to use consts in math
pi = 7;     // illegal - you can't write to (modify) a constant

Notes and Warnings

#define or const

You can use either const or #define for creating numeric or string constants. For arrays, you will need to use const. In general const is preferred over #define for defining constants.

See also